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1.
Improved legume tree fallows have great potential to increase soil organic carbon (SOC), aggregate stability and soil infiltration rates during the fallowing phase. However, persistence of the residual effects of improved fallowing on SOC, aggregate stability and infiltration rates, under different tillage systems in Zimbabwe is not well documented. The relationships between SOC, aggregate stability and infiltration in fallow-maize rotation systems are also not well documented. We therefore evaluated effects of tillage on SOC, aggregate stability and infiltration rates of a kaolinitic sandy soil during the cropping phase of an improved fallow-maize rotation system. Plots that were under legume tree fallows (Sesbania sesban; Acacia angustissima), natural fallow (NF) and under continuous maize during the previous 2 years were divided into conventional tillage (CT) and no-till (NT) subplots soon after fallow termination, and maize was cropped in all plots during the following two seasons. Aggregate stability was investigated using water stable macroaggregation index (Ima), water dispersible clay (WDC) and using the mean weight diameter (MWD) after different wetting procedures. Infiltration rates were determined using simulated rainfall at intensity of 35 mm h−1 on 1 m2 plots. Soil organic carbon was significantly higher (P < 0.05) under fallows than continuous maize. For the 0–5 cm depth SOC was 11.0, 10.0, 9.4 and 6.6 g kg−1 for A. angustissima, S. sesban, NF and continuous maize, respectively, at fallow termination. After 2 years of cropping SOC was 8.0, 7.0, 6.1 and 5.9 g kg−1 under CT and 9.1, 9.0, 8.0 and 6.0 g kg−1 under NT for A. angustissima, S. sesban, NF and continuous maize, respectively. Aggregate stability was significantly greater (P < 0.05) under fallows than under continuous maize and also higher under NT than under CT. The macroaggregation index (Ima) for the 0–5 cm depth was 466, 416, 515 and 301 for A. angustissima, S. sesban, NF and continuous maize, respectively at fallow termination, decreasing to 385, 274, 286 and 255 under CT and 438, 300, 325 and 270 under NT, for A. angustissima, S. sesban, NF and continuous maize, respectively, after 2 years of cropping. Percent WDC was also significantly lower (P < 0.05) in fallows than in continuous maize, and for the 0–5 cm it was 11, 10, 8 and 17 for A. angustissima, S. sesban, NF and continuous maize, respectively at fallow termination. After 2 years of cropping WDC (%) was 12, 14, 15 and 17 under CT and 10, 12, 12 and 16 under NT for A. angustissima, S. sesban, NF and continuous maize, respectively. MWD also showed significantly higher (P < 0.05) aggregate stability in fallows than in continuous maize. Water infiltration rates were significantly greater under fallows than continuous maize but these declined significantly during the cropping phase in plots that had been fallowed. In October 2000, infiltration rates in the A. angustissima and NF plots were above 35 mm h−1 as no runoff was observed. Steady-state infiltration rates were 24 mm h−1 in S. sesban and 5 mm h−1 for continuous maize after 30 min of rainfall simulations. After 2 years of cropping infiltration rates remained above 35 mm h−1 in A. angustissima plots, but declined to 18 and 8 mm h−1 for NF, CT and NT respectively and 12 mm h−1 for S. sesban, CT and NT. It is concluded that legume tree fallows improved SOC, aggregate stability and infiltration rates, but these benefits accrued during fallowing decreased significantly after 2 years of cropping following the termination of fallows. The decrease in SOC and aggregate stability was higher under CT than NT. Coppicing fallows of A. angustissima were the best long-term fallow species when integrated with NT as improved soil physical properties were maintained beyond 2 years of post-fallow cropping.  相似文献   

2.
The controls on uptake and release of CO2 by tropical rainforests, and the responses to a changing climate, are major uncertainties in global climate change models. Eddy-covariance measurements potentially provide detailed data on CO2 exchange and responses to the environment in these forests, but accurate estimates of the net ecosystem exchange of CO2 (NEE) and ecosystem respiration (Reco) require careful analysis of data representativity, treatment of data gaps, and correction for systematic errors. This study uses the comprehensive data from our study site in an old-growth tropical rainforest near Santarem, Brazil, to examine the biases in NEE and Reco potentially associated with the two most important sources of systematic error in Eddy-covariance data: lost nighttime flux and missing canopy storage measurements. We present multiple estimates for the net carbon balance and Reco at our site, including the conventional “u* filter”, a detailed bottom-up budget for respiration, estimates by similarity with 222Rn, and an independent estimate of respiration by extrapolation of daytime Eddy flux data to zero light. Eddy-covariance measurements between 2002 and 2006 showed a mean net ecosystem carbon loss of 0.25 ± 0.04 μmol m−2 s−1, with a mean respiration rate of 8.60 ± 0.11 μmol m−2 s−1 at our site. We found that lost nocturnal flux can potentially introduce significant bias into these results. We develop robust approaches to correct for these biases, showing that, where appropriate, a site-specific u* threshold can be used to avoid systematic bias in estimates of carbon exchange. Because of the presence of gaps in the data and the day–night asymmetry between storage and turbulence, inclusion of canopy storage is essential to accurate assessments of NEE. We found that short-term measurements of storage may be adequate to accurately model storage for use in obtaining ecosystem carbon balance, at sites where storage is not routinely measured. The analytical framework utilized in this study can be applied to other Eddy-covariance sites to help correct and validate measurements of the carbon cycle and its components.  相似文献   

3.
Closure of the surface energy balance provides an objective criterion for evaluating eddy-covariance (EC) flux measurements. This study analyses 5 years of EC carbon dioxide, water vapor, and sensible heat flux measurements from three mature boreal forest stands in central Saskatchewan, Canada. The EC sensible and latent heat fluxes, H and λE, underestimated the surface available energy by 11% (aspen), 15% (black spruce), and 14% (jack pine). At all sites, the energy-closure fraction CF responded similarly to the friction velocity u*, atmospheric stability, and time of day. At night, CF increased from 0.3 at very low-u* to an asymptotic maximum of 0.9 at u* above 0.35 m s−1. During unstable-daytime periods, CF varied linearly from 0.7 at low-u* to 1.0 at high-u*. The energy imbalance pattern was similar among sites and may be characteristic of the continental, boreal forest.EC measurements of net ecosystem exchange FNEE have no objective, diagnostic parameter that is equivalent to CF. We therefore derived an analogous FNEE “closure fraction” CFNEE by normalizing measured FNEE against estimates from an empirical model that was tuned to the high-u* data. CF and CFNEE responded similarly to u*, atmospheric stability, and time of day. We discuss two implications for EC flux data post-processing. The results uphold the common practice of rejecting EC measurements during low-u* periods. They also lend support to the application of energy-closure adjustments to H, λE, and FNEE.  相似文献   

4.
Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha−1, PON 0.10–0.30 Mg N ha−1, and PNM 4.6–9.4 kg N ha−1 greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha−1 yr−1 in NTCW to 46 kg N ha−1 yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.  相似文献   

5.
In Vertisols of central India erratic rainfall and prevalence of drought during crop growth, low infiltration rates and the consequent ponding of water at the surface during the critical growth stages are suggested as possible reasons responsible for poor yields (<1 t ha−1) of soybean (Glycine max (L.) Merr.). Ameliorative tillage practices particularly deep tillage (subsoiling with chisel plough) can improve the water storage of soil by facilitating infiltration, which may help in minimizing water stress in this type of soil. In a 3-year field experiment (2000–2002) carried out in a Vertisol during wet seasons at Bhopal, Madhya Pradesh, India, we determined infiltration rate, root length and mass densities, water use efficiency and productivity of rainfed soybean under three tillage treatments consisting of conventional tillage (two tillage by sweep cultivator for topsoil tillage) (S1), conventional tillage + subsoiling in alternate years using chisel plough (S2), and conventional tillage + subsoiling in every year (S3) as main plot. The subplot consisted of three nutrient treatments, viz., 0% NPK (N0), 100% NPK (N1) and 100% NPK + farmyard manure (FYM) at 4 t ha−1 (N2). S3 registered a significantly lower soil penetration resistance by 22%, 28% and 20%, respectively, at the 17.5, 24.5 and 31.5 cm depths over S1 and the corresponding decrease over S2 were 17%, 19% and 13%, respectively. Bulk density after 15 days of tillage operation was significantly low in subsurface (15–30 cm depth) in S3 (1.39 mg m−3) followed by S2 (1.41 mg m−3) and S1 (1.58 mg m−3). Root length density (RLD) and root mass density (RMD) of soybean at 0–15 cm soil depth were greater following subsoiling in every year. S3 recorded significantly greater RLD (1.04 cm cm−3) over S2 (0.92 cm cm−3) and S1 (0.65 cm cm−3) at 15–30 cm depth under this study. The basic infiltration rate was greater after subsoiling in every year (5.65 cm h−1) in relation to conventional tillage (1.84 cm h−1). Similar trend was also observed in water storage characteristics (0–90 cm depth) of the soil profile. The faster infiltration rate and water storage of the profile facilitated higher grain yield and enhanced water use efficiency for soybean under subsoiling than conventional tillage. S3 registered significantly higher water use efficiency (17 kg ha−1 cm−1) over S2 (16 kg ha−1 cm−1) and S1 (14 kg ha−1 cm−1). On an average subsoiling recorded 20% higher grain yield of soybean over conventional tillage but the yield did not vary significantly due to S3 and S2. Combined application of 100% NPK and 4 t farmyard manure (FYM) ha−1 in N2 resulted in a larger RLD, RMD, grain yield and water use efficiency than N1 or the control (N0). N2 registered significantly higher yield of soybean (1517 kg ha−1) over purely inorganic (N1) (1392 kg ha−1) and control (N0) (898 kg ha−1). The study indicated that in Vertisols, enhanced productivity of soybean can be achieved by subsoiling in alternate years and integrated with the use of 100% NPK (30 kg N, 26 kg P and 25 kg K) and 4 t FYM ha−1.  相似文献   

6.
Field experiments were conducted at Fort Vermilion (58°23′N 116°02′W), Alberta, to determine phosphorus (P) release patterns from red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues in the 7th and 8th years of conventional and zero tillage. Phosphorus contained in crop residues ranged from 1.5 kg ha−1 in pea to 9.2 kg ha−1 in clover GM, both under zero tillage. The patterns of P release over a 52-week period sometimes varied with tillage, i.e., a greater percentage of GM residue P was released under conventional tillage than under zero tillage in the first 2–10 weeks of residue placement. Wheat residues resulted in net P immobilization under zero tillage, but the amounts immobilized were less than 1 kg ha−1. When net P mineralization occurred, the percentage of P released ranged from 24% of wheat P under conventional tillage to 74% of GM P under conventional tillage. The amounts of P released were 0.4 kg ha−1 from wheat, 0.8 kg ha−1 from canola, 0.4 kg ha−1 from pea and 5.1–5.6 kg ha−1 from clover GM residues. Therefore, only GM residues recycled agronomically significant amounts of P for use by subsequent crops in rotation. Phosphorus release was positively correlated with residue P concentration and negatively correlated with C/P and lignin/P ratios.  相似文献   

7.
Nitrous oxide (N2O) and methane (CH4) emitted by anthropogenic activities have been linked to the observed and predicted climate change. Conservation tillage practices such as no-tillage (NT) have potential to increase C sequestration in agricultural soils but patterns of N2O and CH4 emissions associated with NT practices are variable. Thus, the objective of this study was to evaluate the effects of tillage practices on N2O and CH4 emissions in long-term continuous corn (Zea mays) plots. The study was conducted on continuous corn experimental plots established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. The experimental design consisted of NT, chisel till (CT) and moldboard plow till (MT) treatments arranged in a randomized block design with four replications. The N2O and CH4 fluxes were measured for 1-year at 2-week intervals during growing season and at 4-week intervals during the off season. Long-term NT practice significantly decreased soil bulk density (ρb) and increased total N concentration of the 0–15 cm layer compared to MT and CT. Generally, NT treatment contained higher soil moisture contents and lower soil temperatures in the surface soil than CT and MT during summer, spring and autumn. Average daily fluxes and annual N2O emissions were more in MT (0.67 mg m−2 d−1 and 1.82 kg N ha−1 year−1) and CT (0.74 mg m−2 d−1 and 1.96 kg N ha−1 year−1) than NT (0.29 mg m−2 d−1 and 0.94 kg N ha−1 year−1). On average, NT was a sink for CH4, oxidizing 0.32 kg CH4-C ha−1 year−1, while MT and CT were sources of CH4 emitting 2.76 and 2.27 kg CH4-C ha−1 year−1, respectively. Lower N2O emission and increased CH4 oxidation in the NT practice are attributed to decrease in surface ρb, suggesting increased gaseous exchange. The N2O flux was strongly correlated with precipitation, air and soil temperatures, but not with gravimetric moisture content. Data from this study suggested that adoption of long-term NT under continuous corn cropping system in the U.S. Corn Belt region may reduce GWP associated with N2O and CH4 emissions by approximately 50% compared to MT and CT management.  相似文献   

8.
To date, tillage erosion experiments in Canada have only been conducted on conventionally tilled corn-based production systems in Ontario and conventionally tilled cereal-based production in Manitoba. Estimates and assumptions have been made for all other production systems. Therefore, the objective of this study was to evaluate the erosivity of primary and secondary tillage operations within conventional and conservation potato production systems used in Atlantic Canada. Regression analysis determined that a direct relationship exists between slope gradient and both the mean displacement distance of the tilled layer (TL) and the mass of translocated soil (TM) for the chisel plough (CP), mouldboard plough (MP) and offset disc (OD), but not for the vibrashank (VS). Overall, the potential for tillage erosion of the MP, CP, and OD was similar (1.8–1.9 kg m−1 %−1 pass−1) and larger than that of the VS (0.3 kg m−1 %−1 pass−1). The regression coefficients for each implement were improved after including slope curvature, and we recommend that curvature be included in any future tillage erosion modelling. Our results show that both residue management to control wind and water erosion and soil movement to control tillage erosion must be considered when choosing implements and developing best management practices with regards to reducing the negative impacts of total soil erosion on potato production systems in Atlantic Canada.  相似文献   

9.
Reiji Kimura  Long Bai  Jiemin Wang 《CATENA》2009,77(3):292-296
We analyzed relationships among dust outbreaks, Normalized Difference Vegetation Indices (NDVI), and surface soil water content (0 to 2 cm depth) on the Loess Plateau, a significant dust source area of East Asia. World Surface Data for wind speed and current weather, coarse-resolution data for NDVI, and a three-layer soil model for surface soil water content were used. The threshold NDVI for preventing dust outbreaks was about 0.2 when the wind speed ranged from 7 to 8 m s− 1. This threshold NDVI corresponds to a vegetation cover of 18%. The threshold ratio of surface soil water content to the field capacity (θr) was about 0.2. Conditions facilitating dust outbreaks on the Loess Plateau are when NDVI is less than 0.2 with wind speed  7 m s− 1 and θr < 0.2, and when NDVI is greater than 0.2 with wind speed  9 m s− 1 and θr < 0.2.  相似文献   

10.
One of the key issues to increase soil productivity in the Sahel is to ensure water infiltration and storage in the soil. We hypothesised that reducing tillage from annual to biennial ploughing and the use of organic matter, like compost, would better sustain soil hydraulic properties. The study had the objective to propose sustainable soil fertility management techniques in the cotton–maize cropping systems. The effects of reduced tillage (RT) and annual ploughing (AP) combined with compost application (Co) on soil infiltration parameters were assessed on two soil types. Topsoil mean saturated hydraulic conductivities (Ks) were between 9 and 48 mm h−1 in the Luvisol, while in the Lixisol they were between 18 and 275 mm h−1. In the two soil types compost additions with reduced tillage or with annual ploughing had the largest effect on Ks. Soil hydraulic behaviour was in reasonable agreement with soil pore size distribution (mean values varied from 19.5 to 237 μm) modified by tillage frequency and organo-mineral fertilization. Already the first 3 years of this study showed that use of organic matter, improved soil infiltration characteristics when annual ploughing was used. Also biennial ploughing showed promising results and may be a useful strategy for smallholders to manage these soils.  相似文献   

11.
The population abundance of free-living and plant-parasitic nematodes was investigated in a long-term rotation/tillage/stubble management experiment at Wagga Wagga Agricultural Institute, New South Wales (NSW), Australia. The treatments were a combination of two crop rotations: wheat (Triticum aestivum)–wheat and wheat–lupin (Lupinus angustifolius); two tillage systems: conventional cultivation (CC) and direct drill (DD); and two stubble management practices: stubble retention (SR) and stubble burnt (SB). Plots of one of the wheat–wheat treatments received urea at 100 kg N ha−1 during the cropping season. Soil samples from 0–5 and 5–10 cm depths were collected in September (maximum tillering), October (flowering) and December (after harvest), 2001, to analyse nematode abundance. Soil collected in September was also analysed for concentrations of total and labile C, and pH levels.Three nematode trophic groups, namely bacteria-feeders (primarily Rhabditidae), omnivores (primarily Dorylaimidae excluding plant-parasites and predators) and plant-parasites (Pratylenchus spp. and Paratylenchus spp.) were recorded in each soil sample. Of them, bacteria-feeders (53–99%, population range 933–2750 kg−1 soil) dominated in all soil samples. There was no difference in nematode abundance and community composition between the 0–5 cm and 5–10 cm layers of soil. The mean population of free-living and plant-parasitic nematodes varied significantly between the treatments in all sampling months. In most cases, total free-living nematode densities (Rhabditidae and Dorylaimidae) were significantly (P < 0.001) greater in wheat–lupin rotation than the wheat–wheat rotation irrespective of tillage and stubble management practices. In contrast, a greater population of plant-parasitic nematodes was recorded from plots with wheat–wheat than the wheat–lupin rotation. For treatments with wheat–wheat, total plant-parasitic nematode (Pratylenchus spp. and Paratylenchus spp.) densities were greater in plots without N-fertiliser (295–741 kg−1 soil) than the plots with N-fertiliser (14–158 kg−1 soil).Tillage practices had significant (P < 0.05) effects mostly on the population densities of plant-parasitic nematodes while stubble management had significant effects (P < 0.05) on free-living nematodes. However, interaction effects of tillage and stubble were significant (P < 0.01) for the population densities of free-living nematodes only. Population of Rhabditidae was significantly higher in conventional cultivated plots (7244 kg−1 soil) than the direct drilled (3981 kg−1 soil) plots under stubble retention. In contrast, plots with direct drill and stubble burnt had significantly higher populations of Dorylaimidae than the conventional cultivation with similar stubble management practice. No correlations between abundance of free-living nematodes, and concentration of total C and labile C in soil were observed in this study. These results showed that stubble retention contributed for enormous population density of free-living (beneficial) nematodes while conventional cultivation, irrespective of stubble management, contributed for suppressing plant-parasitic nematodes.  相似文献   

12.
Abstract

The study aimed at quantifying the rates of soil CO2 efflux under the influence of common tillage systems of moldboard plow (PT), chisel plow (CT), rotary tiller (RT), heavy disc harrow (DT), and no-tillage (NT) for 46 days in October and November in a field left fallow after wheat harvest located in southern Turkey. The NT and DT plots produced the lowest soil CO2 effluxes of 0.3 and 0.7 g m?2 h?1, respectively, relative to the other plots (P < 0.001). Following the highest rainfall amount of 87 mm on the tenth day after the tillage, soil CO2 efflux rates of all the plots peaked on the 12th day, with less influence on soil CO2 efflux in the NT plot than in the conventional tillage plots. Soil evaporation in NT (64 mmol m?2 s?1) was significantly lower than in the PT (85 mmol m?2 s?1) and RT (89 mmol m?2 s?1) tillage treatments (P < 0.01). The best multiple-regression model selected explained 46% of variation in soil respiration rates as a function of the tillage treatments, soil temperature, and soil evaporation (P < 0.001). The tillage systems of RT, PT, and CT led, on average, to 0.23, 0.22, and 0.18 g m?2 h?1 more soil CO2 efflux than the baseline of NT, respectively (P≤0.001).  相似文献   

13.
We studied the influence of different soil tillage and fertilization on chemical parameters, soil structure stability and carbon distribution in water-stable macro-aggregates (WSAma) of loamy Orthic Luvisol. In 1994, the Department of Plant Production of the Slovak Agricultural University in Nitra established a long-term field experiment in locality Dolná Malanta. In 1994–2007, the soil samples were collected from the depth 0–0.3 m. The field experiment included two types of soil tillage (conventional tillage—CT and reduced tillage—RT) and three variants of fertilization (1. Co—without fertilization, 2. PR + NPK—crop residues together with added NPK fertilizers, 3. NPK—with added NPK fertilizers). Different tillage and fertilization had statistically significant influence on changes of the soil pH and soil sorptive complex. The values of pH were more favourable in RT than in CT. In NPK (by 26%) and in PR + NPK (by 21%) decreased values of hydrolytic acidity. On the other hand it increased the sum of basic cations. This led to the increase of cation exchangeable capacity. In comparison to CT, a higher total carbon concentration (Ct) was determined in RT. According to vulnerability coefficient (Kv), the soil structure stability was better in RT (4.64 ± 1.54) than in CT (5.15 ± 1.75). Average value of WSAma was higher by 9% in RT and it led to increasing of the sum of mean weight diameters of water-stable aggregates (MWD-WSA) by 11% and increasing of index stability (Sw) by 12%. We determined linear dependences between Ct and critic level of soil organic matter concentration (St) in CT and RT as well as in PR + NPK and NPK. The negative correlation between Ca2+ and St (−0.507**) and positive correlation between Ca2+ and crusting index (0.525**) were detected in CT. The values of Ca2+ were in positive correlation with crusting index (0.363*) in RT. We observed higher concentrations of Ct and labile carbon content (CL) in water-stable micro-aggregates (WSAmi) and WSAma in the size fractions from 25 × 10−4 to 3 × 10−3 m in RT. There were also higher concentrations of Ct and CL in WSAma in the size fractions >3 × 10−3 m in CT. The application of crop residues together with NPK fertilizers increased the concentration of Ct in all fractions of WSAma. On the other hand, Ct concentration decreased by 7% in WSAmi. In PR + NPK, the highest concentration of CL was observed in WSAma in the size fraction 2 × 10−3 to 3 × 10−3 m.  相似文献   

14.
Previous studies have demonstrated inconsistent results on the impact of tillage systems on nitrogen (N) losses from field-applied manure. This study assessed the impact of no-tillage (NT) and conventional tillage (CT) systems on gaseous N losses, N2O:N2O + N2 ratios and NO3−-N leaching following surface application of cattle manure. The study was undertaken during the 2003/2004 and 2004/2005 seasons at two field sites in Nova Scotia namely, Streets Ridge (SR) in Cumberland County and the Bio-environmental Engineering Centre (BEEC) in Truro. Results showed that the NT system had higher (p < 0.05) NH3 losses than CT. Over the two seasons, manure incorporation in CT reduced NH3 losses on average by 86% at SR and 78% at BEEC relative to NT. At both sites and during both seasons, denitrification rates and N2O fluxes in NT were generally higher than in CT plots, presumably due to higher soil water and organic matter content in NT. Over the two seasons, mean denitrification rates at SR were 239 and 119 g N ha−1 d−1, while N2O fluxes were 120 and 64 g N ha−1 d−1 under NT and CT, respectively. At BEEC mean denitrification rates were 114 and 71 g N ha−1 d−1, while N2O fluxes were 52 and 27 g N ha−1 d−1 under NT and CT, respectively. Conversely, N2O:N2O + N2 ratios were lower in NT than CT suggesting more complete reduction of N2O to N2 under NT. When averaged across all soil depths, NO3−-N was higher (p < 0.05) in CT than NT. Nitrate-N decreased with depth at both sites regardless of tillage. In most cases, NO3−-N was higher under CT than NT at all soil depths. Similarly, flow-weighted average NO3−-N concentrations in drainage water were generally higher under CT. This may be partly attributed to higher denitrification rates under NT. Therefore, NT may be a viable strategy to remove NO3−-N from the soil, and thus, reduce NO3−-N contamination of groundwater. However, it should be noted that while the use of NT reduces NO3−-N leaching it may come with unintended environmental tradeoffs, including increased NH3 and N2O emissions.  相似文献   

15.
Cover crop and tillage effects on soil enzyme activities following tomato   总被引：2，自引：0，他引：2  
Increasing numbers of vegetable growers are adopting conservation tillage practices and including cover crops into crop rotations. The practice helps to increase or maintain an adequate level of soil organic matter and improves vegetable yields. The effects of the practices, however, on enzyme activities in southeastern soils of the United States have not been well documented. Thus, the objectives of the study were to investigate the effects of cover crops and two tillage systems on soil enzyme activity profiles following tomato and to establish relationships between enzyme activities and soil organic carbon (C) and nitrogen (N). The cover crops planted late in fall 2005 included black oat (Avena strigosa), crimson clover (Trifolium incarnatum L.), or crimson clover–black oat mixed. A weed control (no cover crop) was also included. Early in spring 2006, the plots were disk plowed and incorporated into soil (conventional tillage) or mowed and left on the soil surface (no-till). Broiler litter as source of N fertilizer was applied at a rate of 4.6 Mg ha−1, triple super phosphate at 79.0 kg P ha−1, and potassium chloride at 100 kg K ha−1 were also applied according to soil testing recommendations. Tomato seedlings were transplanted and grown for 60 days on a Marvyn sandy loam soil (fine-loamy, kaolinitic, thermic Typic Kanhapludults). Ninety-six core soil samples were collected at incremental depths (0–5, 5–10, and 10–15 cm) and passed through a 2-mm sieve and kept moist to study arylamidase (EC 3.4.11.2), l-asparaginase (EC 3.5.1.1), l-glutaminase (EC 3.5.1.2), and urease (EC 3.5.1.5) activities. Tillage systems affected only l-glutaminase activity in soil while cover crops affected activities of all the enzymes studied with the exception of urease. The research clearly demonstrated that in till and no-till systems, l-asparaginase activity is greater (P ≤ 0.05) in plots preceded by crimson clover than in those preceded by black oat or their mixture. Activity of the enzyme decreased from 11.7 mg NH4+–N kg−1 2 h−1 at 0–5 cm depth to 8.73 mg NH4+–N kg−1 2 h−1 at 5–10 cm and 10–15 cm depths in the no-till crimson clover plots. Arylamidase activity significantly correlated with soil organic C (r = 0.699**) and soil organic N (r = 0.764***). Amidohydrolases activities significantly correlated with soil organic N but only urease significantly correlated with soil organic C (r = 0.481*). These results indicated that incorporation of cover crops into rotations may increase enzyme activities in soils.  相似文献   

16.
To test the assumption that changes to earthworm communities subsequently affect macroporosity and then soil water infiltration, we carried out a 3 year study of the earthworm communities in a experimental site having six experimental treatments: 2 tillage management systems and 3 cropping systems. The tillage management was either conventional (CT; annual mouldboard ploughing up to −30 cm depth) or reduced (RT; rotary harrow up to −7 cm depth). The 3 cropping systems were established to obtain a wide range of soil compaction intensities depending on the crop rotations and the rules of decision making. In the spring of 2005, the impact of these different treatments on earthworm induced macroporosity and water infiltration was studied. During the 3 years of observation, tillage management had a significant effect on bulk density (1.27 in CT and 1.49 mg m−3 in RT) whereas cropping system had a significant effect on bulk density in RT plots only. Tillage management did not significantly affect earthworm abundance but significantly influenced the ecological type of earthworms found in each plot (anecic were more abundant in RT). On the contrary cropping system did have a significant negative effect on earthworm abundance (104 and 129 ind. m−2 in the less and most compacted plots, respectively). Significantly higher numbers of Aporrectodea giardi and lower numbers of Aporrectodea caliginosa were found in the most compacted plots. CT affected all classes of porosity leading to a significant decrease in the number of pores and their continuity. Only larger pores, with a diameter superior to 6 mm, however, were adversely affected by soil compaction. Tillage management did not change water infiltration, probably because the increase in macroporosity in RT plots was offset by a significant increase in soil bulk density. However, cropping system had a significant effect on water infiltration (119 vs 79 mm h−1 in the less and most compacted plots, respectively). In RT plots, a significant correlation was observed between larger macropores (diameter > 6 mm) and water infiltration illustrating the potential positive effect of earthworms in these plots.  相似文献   

17.
Drainage, tillage, and intensive land use lead to drastic alterations in physical characteristics of organic soils. As decomposition and soil formation progress, bulk density (ρb) increases and total porosity (ft) decreases due to subsidence, shrinkage, and mineralization of soil organic matter (SOM). However, the rate of subsidence and the changes in soil properties differ among management systems. Thus, the objectives of this study were to determine the effects of different tillage practices on ρb and ft of cultivated peat soils. These experiments were conducted during 2004–2005, on Histosols in north central Ohio. Soil core samples were obtained from experimental plots managed with moldboard plow (MB), no-till (NT), or left bare (B). Conversion of plow tillage to NT increased ρb from 0.52 to 0.57 Mg m−3, and decreased ft from 0.72 to 0.70 m3 m−3.  相似文献   

18.
Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N2O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced 15N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil Nnew (i.e., N derived from 15N-fertilizer or -15N-cover crop), with 173 kg Nnew ha−1 in the conventional system compared to 71.6 and 69.2 kg Nnew ha−1 in the low-input and organic systems, respectively. In the conventional system, more Nnew was found in the microaggregate and silt-and-clay fractions, whereas, the Nnew of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-Nnew than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-Nnew was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N2O emissions (39.5 g N2O–N ha−1 day−1) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha−1) produced intermediate N2O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N2O emissions, and N availability.  相似文献   

19.
The greenhouse gases CO2 and N2O emissions were quantified in a long-term experiment in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated during 32 years in plots under a maize–wheat rotation. Continuous CO2 and periodical N2O soil emission measurements were performed during two periods: under maize cultivation (April 2003–July 2003) and during the fallow period after wheat harvest (August 2003–March 2004). In order to document the dynamics and importance of these emissions, soil organic C and mineral N, residue decomposition, soil potential for CO2 emission and climatic data were measured. CO2 emissions were significantly larger in NT on 53% and in CT on 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO2 emissions did not differ significantly between CT and NT. However, the cumulated CO2 emissions from August to November 2003 were considerably larger for NT than for CT. Over the entire 331 days of measurement, CT and NT emitted 3160 ± 269 and 4064 ± 138 kg CO2-C ha−1, respectively. The differences in CO2 emissions in the two tillage systems resulted from the soil climatic conditions and the amounts and location of crop residues and SOM. A large proportion of the CO2 emissions in NT over the entire measurement period was probably due to the decomposition of old weathered residues. NT tended to emit more N2O than CT over the entire measurement period. However differences were statistically significant in only half of the cases due to important variability. N2O emissions were generally less than 5 g N ha−1 day−1, except for a few dates where emission increased up to 21 g N ha−1 day−1. These N2O fluxes represented 0.80 ± 0.15 and 1.32 ± 0.52 kg N2O-N ha−1 year−1 for CT and NT, respectively. Depending on the periods, a large part of the N2O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period of measurement after 32 years of tillage treatments, the NT system emitted more greenhouses gases (CO2 and N2O) to the atmosphere on an annual basis than the CT system.  相似文献   

20.
Soil water and nutrients play an important role in increasing sorghum (Sorghum bicolor L. Moench) yields in the Vertisols of semi-arid tropics during post-rainy season. The effects of tillage practices, organic materials and nitrogen fertilizer on soil properties, water conservation and yield of sorghum were evaluated during winter seasons of 1994–1995 and 1995–1996 on deep Vertisols at Bijapur in the semi-arid tropics of Karnataka State (Zone 3) of south India. Conservation and availability of water and nutrients during different stages of crop growth were increased by deeper tillage resulting in increased grain yield of winter sorghum. Medium and deep tillage increased the grain yield by 23% (1509 kg ha−1) and 57% (1919 kg ha−1) during 1994–1995 and 14% (1562 kg ha−1) and 34% (1835 kg ha−1) during 1995–1996, respectively, over shallow tillage. Water use efficiency increased from shallow (4.90 kg ha−1 mm−1) to deep tillage (7.30 kg ha−1 mm−1). Greater water use efficiency during 1994–1995 as compared to 1995–1996 was attributed to lower consumptive use of water during 1994–1995. Among organic materials, application of Leucaena loppings conserved larger amounts of water and increased winter sorghum yield and water use efficiency. Application of Leucaena loppings increased the winter sorghum grain yield by 9% (mean of 1994–1995 and 1995–1996) as compared to vermicompost. Significantly (P < 0.05) higher water use efficiency of 6.32 kg ha−1 mm−1 was observed in Leucaena loppings incorporated plots compared to 5.72 kg ha−1 mm−1 from vermicompost. Grain yield increased by 245 kg ha−1 with application of 25 kg N ha−1 in 1994–1995, and a further increase in N application to 50 kg ha−1 increased the grain yield by about 349 kg ha−1 in 1995–1996. Deep tillage with application of 25 kg N ha−1 resulted in significantly higher sorghum yield (2047 kg ha−1) than control during 1994–1995. Deep tillage with integrated nutrient management (organic and inorganic N sources) conserved higher amount of soil water and resulted in increased sorghum yields especially during drought years.  相似文献   

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